Sporozoites are a key developmental stage in the life cycle of the malaria parasite. They have a dual role in the maintenance of the malaria parasite life cycle because they are infective not only for the vertebrate host, but also for the mosquito salivary glands. Because the hypothesis of this research is that the sporozoite is a legitimate target for intervention efforts to prevent transmission of malaria, cDNA libraries for salivary gland sporozoites and for oocyst-derived sporozoites were constructed to assess sporozoite gene expression that occurs within the mosquito. Initial screening of these libraries resulted in the isolation of three novel Plasmodium gallinaceum cDNAs, Pg4, Pg19, and Pg93, that are currently being characterized. This research proposal is designed to complete the molecular characterization of these genes and to begin the functional characterization of Pg4, an apparent novel sporozoite surface molecule, via a gene knockout strategy. In an effort to discover additional sporozoite stage-specific genes, a cross-species hybridization of a P. falciparum oligo micro-array will be employed to isolate differentially expressed salivary gland sporozoite genes. The specific aims of this research include 1) Complete the molecular characterization of the three novel sporozoite genes, Pg4, Pg19, and Pg93, 2) Characterize, at a molecular and functional level, a tentative P. berghei homolog of Pg4 that has been found following a BLAST search of the Plasmodium spp. gene databases, and 3) Isolate and characterize differentially expressed salivary gland sporozoite genes in an effort to discover additional novel sporozoite molecules. The completion of the above specific aims should provide a clearer understanding of the structure and potential function of the three novel genes during the sporozoite stages of the malaria parasite. The molecular comparison of homologous genes may also provide insight into the intricate relationships that exist within and between different parasite systems. Ultimately, this valuable information may be exploited to provide new additions to the arsenal of weapons available to control or eradicate malaria.